Hot dip coating apparatus

ABSTRACT

A hot dip coating apparatus for coating a metal wire or strip with a molten metal. A bath of molten metal has at least one guide member immersed therein. A cooling chamber is positioned above the guide member and has, at the bottom thereof, a bore through which the wire passes and also has a cooling liquid in the bottom thereof. A liquid supplier is attached to the cooling chamber, and a liquid level control means in the form of a monitor coupled to the liquid supplier keeps the liquid at a predetermined liquid level. The guide member and the cooling chamber are combined in a unitary body. The wire coated with the molten metal is cooled by the cooling liquid while passing through the bore while being guided by the guide member.

United States Patent Hozumi et al.

[54] HOT DIP COATING APPARATUS [72] Inventors: Shiro Hozumi; TerukazuKinugasa, both of Osaka-fu, Japan [73] Assignee: Matsushita ElectricIndustrial Co., Ltd.,

Osaka, Japan [22] Filed: Nov. 24, 1970 211 App]. No.: 92,381

1 18/419, DIG. 19, DIG. 20; 165/40; 62/64; 266/3 R, 4 A; 117/102 L, 102M, 119.2, 119.4; 263/3 MA [56] References Cited UNITED STATES PATENTS752,768 2/1904 Goodwin ..1 18/5 ELECTRONIC TEMPERATURE REGULATOR 1 May23, 1972 Primary Examiner-Morris Kaplan Attorney-Wenderoth, Lind &Ponack [57] ABSTRACT A hot dip coating apparatus for coating a metalwire or strip with a molten metal. A bath of molten metal has at leastone guide member immersed therein. A cooling chamber is positioned abovethe guide member and has, at the bottom thereof, a bore through whichthe wire passes and also has a cooling liquid in the bottom thereof. Aliquid supplier is attached to the cooling chamber, and a liquid levelcontrol means in the form of a monitor coupled to the liquid supplierkeeps the liquid at a predetermined liquid level. The guide member andthe cooling chamber are combined in a unitary body. The wire coated withthe molten metal is cooled by the cooling liquid while passing throughthe bore while being guided by the guide member.

9 Clains, 4 Drawing figures FROMOEOURC E COOLING LIQUID PATENTEDMAY 2 3m2 3 664 2 9 3 SHEELI 0F 3 SHIRO HOZUMI F\G.l INVENTORS TERUKAZUKXNUGASA BY wwgzfl a ATTORNEYS PATENTEDmzawn 3,664,293

SHEET 2 0F 3 FROMOSOURCE COOLING LIQUID I 3 92 9| X '(Y 75+ 12 TINVENTORS FIG. 2 SHIRO HOZUMI TERUKAZU KINUGASA ATTORNEYS PATENTEnmzmz3,664,293 SHEET 3 OF 3 THICKNESS (MICRONS) 9 8 INVENTOIB SHIRO HOZUML oTERUKAZU KINUQAA DISTANCE(mm) v F164 BY W ATTORNEYS FIELD OF THEINVENTION AND PRIOR ART This invention relates to a hot dip coatingapparatus for coating metal wires or strips with a solderable metallayer.

The electrical circuitry for electronic equipment such as computers,radio and television sets, includes a number of electrical componentssuch as resistors, condensers, transistors and packed integratedcircuits. These components are attached to a circuit board and connectedto each other by soldering, usually by dip soldering. It is necessaryfor reliable soldering that terminal leads of the electrical componentshave good solderability. The terminal leads are in the form of wires orstrips plated with a tin-lead alloy. It is well known that goodsolderability requires the plating to have a thickness of more thanmicrons.

In the past, such wires and strips have been coated with a thick layerof plating by an electroplating method. However, it has been ratherdifficult to obtain consistently a thick layer of plating byconventional hot dip coating processes. An electroplated layer, however,is rather porous and not in an eutectic state. These conditions detractfrom good solderability. It is also difficult to produce by anelectroplating process a layer which has a homogeneous compositionconsisting of a plurality of elements, such as tin, lead and bismuth.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is toprovide a hot dip coating apparatus capable of coating a wire or a stripcontinuously with a solderable layer having a large thickness.

A further object of this invention is to provide a hot dip coatingapparatus which makes possible controlling the thickness of thesolderable coating layer.

A further object of this invention is to provide a hot dip coatingapparatus which makes possible the manufacturing of a wire or a stripcoated with a solderable layer having a desired composition.

These objects are achieved by providing a hot dip coating apparatuswhich comprises:

1. a bath of molten metal;

2. at least one guide member immersed in said molten metal;

3. a cooling chamber having, at the bottom thereof, a bore through whichcan be passed a wire or a strip, the cooling chamber having a coolingliquid in the bottom thereof;

4. a liquid supplier coupled to said cooling chamber; and

5. combining means combining the guide member and the cooling chamberinto a unitary body. The wire or the strip coated with the molten metalis cooled by the liquid in said cooling chamber while passing throughsaid bore while being guided by the guide member.

Further features of the present invention and a more thoroughunderstanding thereof may be had by a consideration of certainembodiments of the present invention, which are described in thefollowing specification and illustrated in the attached drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a side elevation view partlyin section of the overall apparatus according to the present invention;

FIG. 2 is a sectional view, on an enlarged scale, taken on line 2-2 ofFIG. 1, illustrating a control device mounted on a molten metal bathforming part of the apparatus according to the present invention;

FIG. 3 is a perspective view, partly broken away, of the control deviceforming part of the apparatus according to the present invention; and

FIG. 4 is a graph showing an example of the relationship between thethickness of the layer coated on the wire and the distance from a bottomsurface of a cover nozzle to the molten metal surface.

DETAILED DESCRIPTION OF THE FIGURES For the purpose of simplicity, thehot dip coating apparatus is herein shown and described as being adaptedto coat a copper wire with a tin-lead solder alloy, which coated wirecan readily be used for terminal leads for electrical components such asresistors, condensers, and transistors. However, it will be apparentthat the apparatus is readily adaptable to the coating of a strip metalbody with various metals and alloys without substantial modification ofthe construction of the apparatus.

Referring to FIG. 1, a molten metal bath 3 is divided into two parts, afirst molten metal bath part 9 and a second molten metal bath part 10,which are in communication with each other through a channel 11. Saidbath 3 is mounted on a base 21. A bracket 22 is secured to an end wall24 of said first bath part 9. A guide pulley 5 is rotatably mounted on ashaft 23 on said bracket 22. A bracket 25 is secured to the two sidewalls 27 of the first bath part 9. Each of the side walls 27 has aconventional electric heater (not shown) attached to the outsidethereof. A sinker roll 6 is rotatably mounted on a shaft 26 on saidbracket 25. A metal pipe 30 connects the two molten metal bath parts 9and 10 and defines channel 11. Pipe 30 opens into bath part 9 throughopening 29 in end wall 28, and opens into bath part 10 through opening31 in wall 32. The side walls 33 and 34 of bath part 10 have flanges 35and 36 along the upper edge thereof, respectively (FIG. 2). Brackets 37and 38 are fixed to the flanges 35 and 36 by set screws 39. Shafts 41and 42 are mounted to said brackets 37 and 38. Sinker rolls 7 and 8 arerotatably mounted on said shafts 41 and 42, respectively. A thermocouple44 is coupled to a conventional electronic temperature regulator (notshown) to maintain the molten tim-lead alloy at a precise predeterminedtemperature. Electric heater strips 45 and 46 are attached to side walls34 and 33, respectively (see FIG. 2). Terminal leads 47 and 49 areconnected with the electronic temperature regulator so that saidelectric heater strips 45 and 46 are actuated by said electronictemperature regulator in association with said thermocouple 44.

A control device 15, to be described in detail hereinafter, is mountedon the second bath part 10 above sinker roll 8.

The molten tin-lead alloy 4 in the first molten metal bath part 9 isheated by the electric heaters on the side walls 27 and maintained at apredetermined temperature close to the temperature of the moltentin-lead alloy 4 in the second molten metal bath part 10. The moltentin-lead alloy 4 contained in the second molten metal bath part 10 isheated and maintained precisely at a predetermined temperature. Sincethe second molten metal bath part 10 has a small capacity, it is rathereasy to control precisely the temperature of said molten tin-lead alloy4 of said second molten metal bath part 10.

In operation, a wire 1 of electrolytic copper is fed from a conventionalwire supplier (not shown) while being subjected to the necessary surfacetreatment. The wire 1 is passed into the first molten metal bath part 9containing the molten tinlead alloy 4 over the upper side of the guidepulley 5. Then said wire 1 is guided beneath the sinker roll 6 andpassed through the channel 11 to the second molten metal bath part 10containing said molten tin-lead alloy 4, passing under the sinker roll7. After passing under said sinker roll 7 and under the sinker roll 8,said wire 1 runs upwardly through the control device 15 where said wire1 is coated with a coating of said molten tin-lead alloy 4 of thedesired thickness and is subsequently cooled. At the time, the cooledwire 12 has a coating 13 of the tin-lead alloy in a pasty state. Saidwire 12 is passed through a secondary cooling means 16 and then cooleddown to room temperature so that said coating 13 is solidified. Afterthat, the wire 17 with the solidified coating 18 of said alloy on thesurface thereof is passed over a guide pulley l9 and then is drawn toany suitable and available winding machine (not shown) capable ofwinding up said wire 17 in the direction shown by arrow 20.

Referring to FIGS. 2 and 3, the control device 15 comprises a housing 54having two guide members 51 and 52in the bottom thereof and spaced oneabove the other, and a cooling chamber 53 on the top of the housing 54.Said housing 54 is cylindrical in shape and has a flange 55 formed onthe outer face thereof. The cylindrical wall of said housing 54 haslarge openings 56 at the bottom thereof so that the fresh molten tinleadalloy 4 can flow into the interior of said housing 54.

The housing 54 is movably mounted on a supporting base 59 by means ofthe flange 55. Said supporting base 59 has a circular recess 60 in thecenter thereof and has a large circular opening 62 formed at the centerof the bottom 61 of said recess 60. Said circular recess 60 is largeenough to accept said flange 55 and is covered by a covering plate 63having a large circular opening 64 formed at the center thereof. Setscrews 66 extend through and fix said covering plate 63 onto saidsupporting base 59. Several ball bearings 67 are positioned between saidcovering plate 63 and the upper surface of said flange 55, and are heldin position in holes 69 in a positioning ring 68 mounted on flange 55,the number of said holes 69 being equal to the number of said bearingballs 67. Several bearing balls 70 are positioned between the undersurface of said flange 55 and the bottom 61 of recess 60, and are heldin position in holes 72 in a positioning ring 71 on the bottom 61, thenumber of said holes 72 being equal to the number of said ball bearings70. Said supporting base 59 is secured to the flanges 35 and 56 byscrews 73 and 74. This arrangement makes it possible for said housing 54to move freely in a true horizontal plane while the axis of said housing54 is being kept in a true vertical position.

The two guide members 51 and 52 are fixed to the inner wall 77 ofhousing 54. The guide members 51 and 52 have respective guide holes 78and 79 formed at the center thereof. The holes 78 and 79 have a diametersufficient to allow the wire 1 to pass tightly therethrough. The twoguide holes 78 and 79 are aligned essentially parallel to the centeraxis of the housing 54. Thus, said two guide holes 78 and 79 can guidethe wire 1 in a direction substantially parallel to said center axis ofsaid housing 54. Said two guide members 51 and 52 are preferably made ofa hard steel such as die steel in order that they will wear well.

Said two guide members 51 and 52 can be replaced by a single guidemember having a large thickness sufficient to guide the wire 1.

A cover nozzle 80 is provided which is in the shape of a disc and isfixed to the inner wall 77 of the housing 54. Said cover nozzle 80 hasan opening 81 formed at the center thereof, the inner diameter of whichis sufficiently large to pass the wire 1 freely. Said cover nozzle 80 ispositioned above the guide members 51 and 52 and is essentially at thelevel of the surface of the molten tin-lead alloy 4 in the second moltenmetal bath part 10.

The cooling chamber 53 is in the shape of a cup, and is joined to thehousing 54 by screw threads 82 formed on the outer surface thereof. Saidcooling chamber 53 has a bore 84 formed at the center of the bottom 83thereof. Said bore 84 is in exact alignment with the guide holes 78 and79. Said cooling chamber 53 is preferably made of thermally insulatingmaterial such as polytetrafluoroethylene.

The wire 1, having a coating 13 of the molten tin-lead alloy 4 on thesurface thereof, is passed and drawn up through said bore 84 in thedirection of the arrow 75, said wire 1 being guided by said guide holes78 and 79. A cooling liquid 85 is provided in said cooling chamber 53,the wire 1 being passed through the liquid 85 to cool said coating 13 onthe wire 1 from the molten state into a pasty state.

It has been discovered according to the present invention that theleakage of said liquid 85 from said cooling chamber 53 through said bore84 can be prevented by adjusting both the depth of said liquid 85 andthe clearance between the inner wall of said bore 84 and said wire 1having the coating 13 thereon.

The clearance which will prevent leakage is dependent upon the surfacetension of said liquid 85. When said liquid 85 has high surface tension,such as water, said clearance can be about 0.15 mm. When the liquid 85has a lower surface tension, said clearance should be less than 0.15 mm.

The depth of liquid which will prevent leakage is also dependent uponthe surface tension of said liquid 85 and in practice ranges from 1 tto5 mm. Said depth is kept at a predetermined value by an automaticfeed-back control means comprising a monitoring member 87 and a liquidsupplier 86. As shown in FIGS. 2 and 3, said liquid supplier 86 and saidmonitoring member 87 are attached to the cooling chamber 53. Saidmonitoring member 87 is in a rod shaped member having approximately thesame diameter as the wire 1, and is preferably made of the same metal asthe wire 1. Said monitoring member 87 extends in liquid-tight relationthrough a bore 94 in the bottom 83 of said cooling chamber 53, andtouches the cover nozzle so that heat energy from said cover nozzle 80flows upwardly through said monitoring member 87. A thermo-couple 96 isattached to said monitoring member 87 at a point 97 on the surfacethereof. Said thermocouple 96 mea sures a temperature which isapproximately the temperature of the coating 13 on the wire 1 at thelevel of the point 97. Said thermocouple 96 is coupled to an electronictemperature regulator 98 coupled to an electromagnetic valve 91 havingan inlet 93 and an outlet 92. As one specific example, a Humphreyquick-dump valve can be used as said electromagnetic valve 91, which ismade by Humphrey Products, Kalamazoo, Mich., U.S.A. Said inlet 93 inconnected with a cooling liquid source (not shown). Referring to FIG. 2,the liquid supplier 86 is in the shape of a small tube having a mouthpiece 88 and a clip 89 attached thereto. Said liquid supplier 86 isattached to the side wall of said cooling chamber 53 by said clip 89. Aflexible tube 90 is attached to said mouth piece 88. The other end ofsaid flexible tube 90 is connected with the outlet 92 of theelectromagnetic valve 91. When said electromagnetic valve 91 is openedby the actuation of said electronic temperature regulator 98, saidliquid supplier 86 feeds liquid from the liquid source to said coolingchamber 53 through said inlet 93, outlet 92 and said flexible tube 90.

The control device 15 operates as follows. The temperature of the wire 1adjacent the bore 84 is much higher than the boiling temperature of saidliquid 85. Therefore, said liquid 85 evaporates due to absorption ofheat energy from the wire 1 having the coating 13 thereon and from themonitoring member 85. The cooling rates of said wire 1 and saidmonitoring member 87 are proportional to the respective surface areas incontact with said liquid 85. A decrease in the depth of said liquid 85results in a decrease in the cooling rates of said wire 1 and themonitoring member 87 and in an increase in the temperature at the point97 The control of said liquid level of said liquid 85 makes it possibleto maintain said coating 13 at a predetermined temperature at the levelof said point 97. Such temperature regulation by an electronictemperature regula tor by automatic feed-back control is described inmany places in the literature, such as Automatic Feedback Control,written by W. Ahrendt and 1F. Taplin, 1951, McGraw-Hill Book Co., Inc.,New York, Toronto and London.

The control device 15 operates in such a way that the wire 1 is drawnupwardly through the guide holes 78 and 79, the opening 81 and the bore84 to the air. During this operation, said wire 1 is coated with acoating 13 which is initially in a molten state and subsequently coolsto a pasty state. Said coating 13 is cooled mostly by absorption of heatby said cooling liquid 85 as latent heat of evaporation. It is,therefore, preferable to use a cooling liquid having a large latent heatof evaporation. Preferably the cooling liquid is a member selected fromthe group consisting of pure water, methyl alcohol, ethyl alcohol, andpropyl alcohol. lt has been discovered according to the presentinvention that when a preferred cooling liquid, as described above, hasincorporated therein another chemical agent selected from the groupconsisting of glycerine, diethylene glycol, ethylene glycol, benzylalcohol, polyvinyl alcohol, and polyvinyl butylal, the resultant coatinghas a higher durability in a high temperature environment.

Even when said wire 1 vibrates mechanically, because the housing 54 ismovably mounted on the supporting base 59, as described hereinbefore, itcan follow the movement of said wire 1 so that the guide holes 78 and 79guide said wire 1 so that it moves exactly in the direction of alignmentof said guide holes 78 and 79 and the bore 84. Such an arrangement canprevent said coating 13 from being damaged by touching the inner wall ofsaid bore 84.

After the treatment of the control device 15, said coating 13 is stillin a pasty state. When said coating 13 is solidified slowly, thesolidified coating has a spangled crystalline structure which isundesirable in some cases. It is preferred to employ a secondary coolingmeans 16, which rapidly cools said The bath part 9 and the bath part 10are filled with a molten tin-lead alloy having a composition of weightpercent of tin and 70 weight percent of lead. The second molten metalbath part 10 is maintained within about 1 of 290 C. The diameter of theguide holes 78 and 79 is 9.02 mm. The diameter of the opening 81 isabout 2 mm. The diameter of the bore 84 is l.20 mm. The wire runningvelocity is 50 meters per minute. The resultant thickness of the coatingon the wire varies with the temperature of said molten tin-lead alloyand the wire running velocity. Besides these two factors, the otherfactor which has the greatest effect is the distance of the bottomsurface of the cover nozzle 80 from the surface of the molten tin-leadalloy in the second molten metal bath part 10. An exemplary rela tionbetween said thickness and said distance is shown in FIG. 4. The effectsof the composition of the cooling liquid 85 on the solderability areshown in Table 2.

TABLE 2 After heating at; 180 C. for

hours Shelf-life test for 6 months Liquid Color change SolderabilityColor change Solderability Glycerine, 10 weight percent. a g wager, 90weighlt percenlty }N0ne.. hxcellent..... N011L.... Excellent. Et ylenoglyco 5 weig 1 p Water, Qiwzightgercenfi t. llenzyl a co ol 2 Weig tpercen 1 Methyl alcohol, 80 weight percent.. Distilled water Darkyellow- Fairly good. ..do Do. Methyl alcohol Slightly yellow.. Good .doD0.

wire 12 having said coating 13 thereon by a stream of water. 30

Referring to H6. 1, said secondary cooling means 16 comprises a jet ofwater 115 flowing from an outlet 116 to a receiver 117. Said outlet 116is connected to any suitable and available water pump (not shown) bypiping, in order that said water 115 can flow rapidly from said outlet116 into said receiver 117 without falling to the second molten metalbath part 10. Said water is received by said receiver 117, and isdischarged to the outside through piping (not shown). Said receiver 117and said outlet 116 are secured to a supporting pole 40 by a bracket118. Said wire 12 having said coating 13 which is still in the pastystate is passed through said jet of water 115 and said coating 13 issolidified rapidly thereby to a solid alloy having a eutectic structure.

It is further preferred to employ, in advance of said secondary coolingmeans, a compressing means to compress said coating 13 while it is inthe pasty state. Such compressing means can be any available andsuitable conventional pinch rollers.

When the hot dip coating apparatus according to the present invention isused for coating a wire with an elementary metal or an alloy having aneutectic composition, the secondary cooling means 16 can be omittedsince such metals and alloys can be directly transformed from the moltenstate into the solid metal or alloy by cooling. For such uses, thetemperature of the molten metal or alloy within the second molten metalbath part 10 is maintained at about 10 above the melting pointtemperature of the metal or an alloy so that the cooling liquid 85 inthe cooling chamber 53 can quench the coating 13 of such metal or alloyand transform it from the molten state directly to a solid state.

Further features of the present invention and a more thoroughunderstanding thereof may be had by a consideration of an exemplaryoperation of the hot dip coating apparatus embodying the invention andof exemplary results obtained by using said hot dip coating apparatus.

An electrolytic copper wire having a diameter of 1 mm. is initiallysurface-treated by a flux having a composition as shown in Table 1.

TABLE 1 THE COMPOSITION OF THE FLUX chlorine 6.0% by weight zinc l.3% byweight ammonium 0.3% by weight surfactant 1.0% by weight water 91.4% byweight The hot dip coating apparatus according to the present inventionhas been described as being adapted to coat a copper wire with atin-lead solder alloy. However, the apparatus is readily adaptable forcoating a metal strip body with any desirable metal or alloy withoutsubstantial modifications in the construction of the apparatus. In sucha case, the guide holes 78 and 79, the opening 81, and the bore 84 aremade similar in shape to the cross section of the strip body.

While a particular embodiment of this invention has been shown anddescribed, it will, of course, be apparent that various modificationsmay be made without departing from the invention.

What is claimed is:

1. A hot dip coating apparatus for coating metal wire or strip withmolten metal, comprising:

1. a bath for molten metal;

2. at least one guide member disposed in said bath at a level to beimmersed in molten metal in said bath for guiding wire or strip in agenerally vertical direction;

3. a cooling chamber disposed above said guide member and having in thebottom thereof a bore for passing wire or strip therethrough, saidchamber having a cooling liquid therein, and said bore of a dimension sothat surface tension retains said liquid in the chamber;

4. a tubular member supporting both said guide and said chamber thereinin an aligned'vertical arrangement;

5. a peripheral flange element extending transversely from said tubularmember;

6. a closure element disposed above said bath and having a control boretherethrough and a peripheral slot in the bore wall, whereby toslidingly receive said flange;

7. said flange and slot being so dimensioned whereby the fixed assemblyof said tubular support member, said cooling chamber and said guidemeans are laterally free floating; and

8. a cooling liquid supplier on said cooling chamber for supplyingcooling liquid to said cooling chamber, whereby wire or strip, whilebeing guided by said guide member, is coated with molten metal from thebath and then is cooled by said cooling liquid in said cooling chamberafter passing through said bore into said cooling chamber.

2. A hot dip coating apparatus as claimed in claim 1 further comprisingliquid level control means in said cooling chamber and coupled to andcontrolling said cooling liquid supplier to supply cooling liquid tokeep a predetermined depth of cooling liquid in said cooling chamber.

3. A hot dip coating apparatus as claimed in claim 2 in which saidliquid level control comprises a monitoring member in said coolingchamber which detects the temperature of the coated wire adjacent tosaid liquid and which is coupled to said cooling liquid supplier tocause said cooling liquid supplier to supply sufficient cooling liquidto maintain said temperature at a predetermined value.

4. A hot dip coating apparatus as claimed in claim 1 wherein said guidemember includes a guide having a bore therethrough through which thewire or strip is guided and a cover nozzle mounted above and spaced fromsaid guide.

5. A hot dip coating apparatus as claimed in claim 1 wherein said bathhas two parts and a pipe is connected between said two parts adjacentthe bottoms thereof to provide a channel of molten metal between saidparts.

6. A hot dip coating apparatus as claimed in claim 1 wherein saidcooling liquid consists essentially of a liquid having large latent heatof evaporation.

7. A hot dip coating apparatus as claimed in claim 6 wherein said liquidconsists essentially of one member selected from the group consisting ofpure water, methyl alcohol, ethyl alcohol, and propyl alcohol.

8. A hot dip coating apparatus as claimed in claim 7 wherein said liquidfurther includes one member selected from the group consisting ofglycerine, diethylene glycol, ethylene glycol, benzyl alcohol, polyvinylalcohol, and polyvinyl butylal.

9. A hot dip coating apparatus as claimed in claim 1 which furthercomprises a secondary cooling means mounted above said cooling chamberfor cooling the coated wire down to room temperature.

2. A hot dip coating apparatus as claimed in claim 1 further comprisingliquid level control means in said cooling chamber and coupled to andcontrolling said cooling liquid supplier to supply cooling liquid tokeep a predetermined depth of cooling liquid in said cooling chamber. 2.at least one guide member disposed in said bath at a level to beimmersed in molten metal in said bath for guiding wire or strip in agenerally vertical direction;
 3. a cooling chamber disposed above saidguide member and having in the bottom thereof a bore for passing wire orstrip therethrough, said chamber having a cooling liquid therein, andsaid bore of a dimension so that surface tension retains said liquid inthe chamber;
 3. A hot dip coating apparatus as claimed in claim 2 inwhich said liquid level control comprises a monitoring member in saidcooling chamber which detects the temperature of the coated wireadjacent to said liquid and which is coupled to said cooling liquidsupplier to cause said cooling liquid supplier to supply sufficientcooling liquid to maintain said temperature at a predetermined value. 4.A hot dip coating apparatus as claimed in claim 1 wherein said guidemember includes a guide having a bore therethrough through which thewire or strip is guided and a cover nozzle mounted above and spaced fromsaid guide.
 4. a tubular membeR supporting both said guide and saidchamber therein in an aligned vertical arrangement;
 5. a peripheralflange element extending transversely from said tubular member;
 5. A hotdip coating apparatus as claimed in claim 1 wherein said bath has twoparts and a pipe is connected between said two parts adjacent thebottoms thereof to provide a channel of molten metal between said parts.6. A hot dip coating apparatus as claimed in claim 1 wherein saidcooling liquid consists essentially of a liquid having large latent heatof evaporation.
 6. a closure element disposed above said bath and havinga control bore therethrough and a peripheral slot in the bore wall,whereby to slidingly receive said flange;
 7. said flange and slot beingso dimensioned whereby the fixed assembly of said tubular supportmember, said cooling chamber and said guide means are laterally freefloating; and
 7. A hot dip coating apparatus as claimed in claim 6wherein said liquid consists essentially of one member selected from thegroup consisting of pure water, methyl alcohol, ethyl alcohol, andpropyl alcohol.
 8. A hot dip coating apparatus as claimed in claim 7wherein said liquid further includes one member selected from the groupconsisting of glycerine, diethylene glycol, ethylene glycol, benzylalcohol, polyvinyl alcohol, and polyvinyl butylal.
 8. a cooling liquidsupplier on said cooling chamber for supplying cooling liquid to saidcooling chamber, whereby wire or strip, while being guided by said guidemember, is coated with molten metal from the bath and then is cooled bysaid cooling liquid in said cooling chamber after passing through saidbore into said cooling chamber.
 9. A hot dip coating apparatus asclaimed in claim 1 which further comprises a secondary cooling meansmounted above said cooling chamber for cooling the coated wire down toroom temperature.